documentclass[landscape]{article}
pagestyle{plain}
usepackage[hmargin=1cm, vmargin=2cm]{geometry}

usepackage{longtable}
usepackage{booktabs}
usepackage{array}
usepackage{threeparttable}
usepackage[referable]{threeparttablex}
usepackage{arydshln}

LTpre0ptLTpost0pt
LTleft1emLTright1em
newlengthtabcolwidth
newlengthfirstcoltext
newlengthrowheight
setlength{footskip}{0pt}
setlength{rowheight}{13ex}
newcolumntype{y}[1]{>{raggedrightarraybackslash}p{#1}}

begin{document}
centeringlarge
LTcapwidth=textwidth
settowidthfirstcoltext{longest~}
setlengthtabcolwidth{dimexpr.5textwidth-firstcoltext-tabcolsep-10pt}
begin{ThreePartTable}
  % renewcommandTPTminimum{textwidth}
  begin{TableNotes}
    item[a] label{tn:a} foo
    item[b] label{tn:b} bar
    % unskipstrutpar
  end{TableNotes}
  begin{longtable}{%
      @{extracolsep{fill}}ry{tabcolwidth}:y{tabcolwidth}@{}}
      caption{Please fill in this table.}\
      toprule
      multicolumn{1}{r}{~}
      & multicolumn{1}{y{tabcolwidth}}{A}
      & multicolumn{1}{y{tabcolwidth}}{B} \
    midrule
    endhead
    cmidrule{3-3}
    multicolumn{3}{r}{raggedlefttextit{continued ldots}}
    endfoot
    bottomrule
    insertTableNotes\
    endlastfoot
    multicolumn{1}{r:}{foo} & & \[rowheight]cdashline{2-3}
    longesttnotex{tn:a} & & \[rowheight]cline{1-3}
    foo & & \[rowheight]cdashline{2-3}
    bartnotex{tn:b} & & \[rowheight]cdashline{2-3}
    baz & & \[rowheight]
  end{longtable}
end{ThreePartTable}
end{document}